Device and method for producing hollow plastic bodies

ABSTRACT

An apparatus for producing hollow bodies, in particular bottles and similar containers provided with an evacuation opening, of thermoplastic includes a lower machine part and a beamlike upper machine part. The lower machine part is equipped with at least two blow molds, each provided with a cavity. A number of blowing and calibration mandrels corresponding to the number of blow molds is disposed on the beamlike upper machine part disposed above the lower machine part. One blow mold is assigned to each blowing and calibration mandrel. The blowing and calibration mandrels can be axially fed jointly toward the blow molds and can be moved with their calibration region into an orifice of the cavity until an annular shoulder of the blowing and calibration mandrels comes into contact with a counterpart face on the associated blow mold. The blowing and calibration mandrels are retained axially freely movably, within predeterminable limits, in the upper machine part. Upon joint feeding of the blowing and calibration mandrels toward the blow molds, the blowing and calibration mandrels are automatically adjustable in height relative to their outset position, counter to the resistance of a coupling medium.

RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §§119 and 365 to Swissapplication 337/00 filed in Switzerland on Feb. 22, 2000, andPCT/CH01/00016 filed as an International Application on Jan. 9, 2001,the entire contents of which are hereby incorporated by reference.

BACKGROUND

1. Field of the Invention

The invention relates to an apparatus for producing hollow bodies ofthermoplastic. The invention also relates to a method for producinghollow bodies of a plastic in a hollow body blowing process.

2. Background Information

The containers of tinned sheet-iron or mixed sheet metal, glass, orceramic that were typical in the past are increasingly being replacedwith plastic containers. Especially for packaging fluid substances, suchas beverages, oil, cleaning utensils, cosmetics, and so forth, plasticcontainers are used primarily. The low weight and lower costs surelyplay a not inconsiderable role in this substitution. The use ofrecyclable plastic materials and the overall more-favorable totalexpenditure of energy for producing them also contribute to increasingconsumer acceptance of plastic containers, especially plastic bottles.

The production of plastic containers, especially plastic bottles, isdone by extrusion blowing, in particular hollow body blowing, forinstance tubular film blowing. In this process, a preform such as atube, extruded in a single layer or multiple layers, is placed in blowmolds, inflated by overpressure via a blow mandrel, and hardened bycooling. The automatic blow molder used for this purpose as a rule has aplurality of parallel-connected blow molds, which make it possible toproduce a plurality of plastic containers simultaneously in oneoperation. Each blow mold is assigned a separate blow mandrel, which canbe put into position in a way suitable for the process.

In many cases, hollow plastic bodies, such as bottles or canisters, butalso industrial parts, have one or more openings, which are for aparticular purpose in later use. Often such openings are embodied suchthat they are closable by suitable closing devices. These can forinstance be screw closures or snap closures. An essential demand theclosing technology must meet is tightness to liquids, gases and solidsin powdered or granular form. In plastic packages, the tightness istypically achieved by creating smooth, dimensionally accurate sealingfaces adapted to one another in both the hollow body and the closure. Itis known that the sealing quality can be improved still further by thechoice of the correct combination of materials for the hollow body andthe closure.

Producing openings designed in this way typically is done simultaneouslywith the process of producing the hollow body. In it, the opening forintroducing the inflation medium that generates the overpressure, whichin most cases is compressed air, is designed at the same time such thatit also meets the later demands made in terms of the use of the hollowbody. In these cases, the sealing faces, which can be present both onthe end face and on the preferably cylindrical or conical inner wall ofa neck extending around the edge of the opening, must be produced. Thisis done in a so-called calibration operation, that is, by means of adimensional adaptation of a portion of the blow mandrel, acting as acalibrating device, with the orifice region of the blow molds and withthe predetermined wall thickness of the preform placed in the blowmolds. The blowing and calibration mandrel furthermore has the task ofpinching off process-created protruding parts of the preform in theupper edge region of the orifice, except for a minimal residualthickness of the hollow body, so that they can be pinched off perfectlyin a deburring process following the inflation operation.

For both operations, that is, calibrating the opening and pinching offprotruding parts, it is necessary for the blowing and calibrationmandrel to assume a very accurate, replicable position in three planesrelative to the orifice of the blow mold. In particular, the axis of theblowing and calibration mandrel must match the axis of the orifice ofthe cavity in the blow mold; the cutting ring face of the blowing andcalibration mandrel must be parallel to the neck blade face of the blowmold, and the terminal height position of the blowing and calibrationmandrel relative to the orifice of the blow mold must always assumeexactly the position in which not only the dimensional tolerances of thefinished hollow body are adhered to but also the pinching off of theprotruding parts is assured. In practice, this is achieved by adjustinga mechanical end stop for the blowing and calibration mandrel. Theadjustment is done manually, in accordance with a visual assessment ofthe pinching-off operation and dimensional checking of the orifice ofthe hollow body by the operator or operators. In a single blowing devicethat has only a single blowing and calibration mandrel, both demands interms of quality can still be met relatively simply and simultaneouslywith regard to the opening and to the protruding parts. In automaticblow molders with a plurality of parallel blow molds and blowing andcalibration mandrels associated with them, however, the adjustingoperation can be accomplished only with great difficulty and is verytime-consuming. In view of the demands for quality made of thepinching-off operation, the individual blowing and calibration mandrelsmust all be adjusted to the correct height relative to the orifices ofthe cavities in the blow molds. In this respect it must be noted thatdimensional differences at the orifices of the individual blow molds,already dictated by the usual production tolerances or by wear, makedifferent height adjustments of the blowing and calibration mandrelsunavoidable. Because of the risk of injury to the operator, themechanically cooperating components of these multiple automatic blowmolders are protected against unauthorized or unintentional access bycovering devices. However, these protective structural provisions are anobstacle to practicable adjustment, which should advantageously be donewith the machine running.

SUMMARY OF THE INVENTION

It is an object of the present invention to overcome disadvantages ofthe apparatuses in the prior art. An apparatus for producing hollowbodies of plastic is to be created in which the adjustment operationsare simplified, and safe, malfunction-free production of hollow bodies,especially plastic bottles and similar containers, of the desiredquality is made possible.

These objects are attained in an apparatus and method for producinghollow bodies of thermoplastic.

An apparatus for producing hollow bodies, in particular bottles andsimilar containers provided with an evacuation opening, of thermoplasticincludes a lower machine part and a beamlike upper machine part. Thelower machine part is equipped with at least two blow molds, eachprovided with a cavity. A number of blowing and calibration mandrelscorresponding to the number of blow molds is disposed on the beamlikeupper machine part disposed above the lower machine part. One blow moldis assigned to each blowing and calibration mandrel. The blowing andcalibration mandrels can be jointly fed axially toward the blow moldsand can be moved with their calibration region into an orifice of thecavity until an annular shoulder of the blowing and calibration mandrelscomes into contact with a counterpart face on the associated blow mold.According to exemplary embodiments of the invention, the blowing andcalibration mandrels are retained axially freely movably, withinpredeterminable limits, in the upper machine part. When the blowing andcalibration mandrels are fed jointly toward the blow molds, the blowingand calibration mandrels are automatically adjustable in height relativeto their outset position, counter to the resistance of a couplingmedium.

Because the blowing and calibration mandrels are supported limitedlyaxially adjustably in the upper machine part and are automaticallyadjustable in height upon being fed toward the blow molds, the tediousprocess of performing the adjustment manually can be dispensed with. Bythe self-adjustment of the blowing and calibration mandrels, it isassured that the encompassing annular shoulders on all the blowing andcalibration mandrels are pressed with the same pressing force againstthe associated counterpart faces on the blow molds. Thus to assure cleanpinching off of material protruding from the preform, only the feedingdevice has to be set up once and for all, for all the blowing andcalibration mandrels. The self-adjustment of the blowing and calibrationmandrels takes place automatically, counter to the restoring force ofcoupling media. Once adjusted automatically with respect to height, themount of the blowing and calibration mandrels assures that the correctadjustment is maintained. On the other hand, the holding force of themounts does not hinder an automatic readjustment, for instance requiredbecause of gradual wear to the cooperating faces that occurs duringlong-term operation. As an additional effect of the somewhat elasticadjustability, damping of the feeding operation ensues, which hasadvantages in terms of wear of the cooperating annular shoulders andcounterpart faces.

In an advantageous variant of the invention, the blowing and calibrationmandrels are coupled hydraulically to one another. By the hydrauliccoupling of the blowing and calibration mandrels, the pressurecompensation and the height adjustability of the blowing and calibrationmandrels can be regulated quite simply. The hydraulically coupledblowing and calibration mandrels cooperate with adjusting pistons, whichare limitedly displaceable axially inside bores in the upper machinepart. The pistons are short-circuited to one another by means of ahydraulic fluid, which forms the coupling medium and is disposed insidea reservoir that communicates with the bores. As a result of thedisposition according to the invention, all the blowing and calibrationmandrels communicate with one another via a communicating vessel. Fromthe moment a reaction force takes effect onward, an equalization ofheight occurs, until all the blowing and calibration mandrels exert thesame force on a part to be pinched off. For instance, standard hydraulicoil is used. A degassing device for the hydraulic oil may be provided.When the hydraulic oil is dispensed in the exclusion of air after priorevacuation of the system, then a degassing device can be omitted.

To take appropriate account of the usual production tolerances, wear,and the requisite variously high cutting devices for various materials,the self-adjusting blowing and calibration mandrels have an axial heightadjustability relative to their outset position that can amount forinstance to about 4 mm, and in a variant of the invention preferablyabout 2.5 mm. Naturally, still greater axial adjustment ranges can alsobe provided.

For reasons of assembly technology and because of simple maintenance,the blowing and calibration mandrels are retained releasably in thebeamlike upper machine part. They are advantageously fixed in theirmounts by clamping. Fastening the blowing and calibration mandrels byclamping has the advantage that even deviations from the set-pointoutside diameter can be compensated for quite simply. Warping, as canoccur in conventional screw mounts, in particular, is avoided.

One not inconsiderable advantage of the clamping mount is that it offersthe capability of fixing all the blowing and calibration mandrels intheir mounts with the same clamping force, regardless of any externaldimensional tolerances that occur. The clamping force is selected suchthat the blowing and calibration mandrels cannot adjust unintentionallybecause of their weight and the dynamic forces involved in the processesof motion, but can be adjusted in the desired way by the action of thehydraulic forces. The blowing and calibration mandrels are preferablyprevented from falling out of the upper machine part by means of stops.

A quite expedient structural variant of the clamping mount includes aretaining nut, which is provided with a male thread and can be screwedinto a threaded bore in the upper machine part. The retaining nut has aconical face, which cooperates with a radially compressible clampingelement, preferably a slit cone provided with a conical counterpart faceand comprising an elastic, wear-resistant material, preferably of anindustrial plastic. The cooperating conical faces divert the forceresulting from the tightening moment of the retaining nut, and by theradial narrowing of the clamping element they assure the requisiteclamping force.

Because the clamping mount includes a prestressing element, dimensionaltolerances and nonuniformities in the embodiment of the thread of thethreaded bore in the upper machine part and on the retaining nut can becompensated for. The prestressing element is preferably formed by a cupspring, which in the put-together state is braced on one end in thethreaded bore and on the other, optionally with the interposition of anunderlay shim or washer, on the clamping element. The underlay shim hasthe advantage that the cup spring cannot dig into the somewhat softer,radially compressible clamping element. This reliably counteracts anymispositioning of the cup spring.

The floating mounting of the blowing and calibration mandrels in theupper machine part also offers the opportunity of rotating them abouttheir longitudinal axis, without shifting of the axial positions set.This is advantageous for instance in blowing and calibration mandrelsthat have a cross section other than circular in the calibration region.For example, the blowing and calibration mandrels have a calibrationregion of elliptical cross section.

For the sake of more easily putting blowing and calibration mandrelswith calibration regions of an other than circular cross section intothe correct position relative to the cavity in the blow mold,positioning means are provided in the upper machine part and on theblowing and calibration mandrels. The positioning means preferably eachinclude circumferential knurling or teeth on the blowing and calibrationmandrel and an externally actuatable adjusting pin on the upper machinepart. The circumferential knurling or teeth can have either a uniform ora variable pitch, so as to adjust the blowing and calibration mandrel inpredetermined and even relatively large increments. The adjusting pinsserve to fix the oriented blowing and calibration mandrels in theposition set.

The stop shoulders on the blowing and calibration mandrels areadvantageously provided on interchangeably held cutting rings. Thecutting rings have especially hardened contact faces and cutting edges,so that the pinching-off operation is effected cleanly and reliably, andthe wear to the cooperating components can be kept as slight aspossible. The interchangeability of the cutting rings makes simplereplacement possible as needed, or simple adaptation to requirements,for instance resulting from different wall thicknesses of the preforms.

With a view to modular construction and various possibilities for use ofthe apparatus, it is also highly advantageous if the calibrating portionof the blowing and calibration mandrel is formed by an interchangeablecalibration sleeve. The interchangeable arrangement offers theopportunity as needed of fastening calibration sleeves of relativelylarge diameter, or sleeves with a cross section other than circular, forinstance an elliptical cross section, to the blowing and calibrationmandrels in order to retrofit the apparatus quite simply to therequirements of the particular hollow body to be produced.

In a method for producing hollow bodies, in particular bottles orsimilar containers provided with an evacuation opening, in a hollow bodyblowing process, preforms extruded in a single layer or multiple layersof a thermoplastic, for instance segments of a hose, are placed in blowmolds. The hollow bodies to be produced are inflated by overpressure inaccordance with the cavities enclosed by the blow molds. The evacuationopenings of the hollow bodies are calibrated, and parts protruding pastthe evacuation necks are pinched off. Finally the unmolded hollow bodiesare hardened by cooling. According to the invention, the blowing andcalibration mandrels, during the pinching-off operation, in which anencompassing annular shoulder on each blowing and calibration mandrel ispressed against a counterpart face on the associated blow mold, areautomatically adjusted axially in height relative to their outsetposition, within predeterminable limits, counter to the restoring forceof a coupling medium.

The automatic self-adjustment of the blowing and calibration mandrelssaves the operator the inconvenient, time-consuming and in some casespotentially dangerous adjustment procedure. It suffices if the feedingdevice on the upper machine part is set in a single adjusting step. Theautomatic reregulation of the height of the blowing and calibrationmandrels assures that operative faces on the encompassing annularshoulders of the blowing and calibration mandrels will all be disposedat the same height and also assures uniform imposition of pressure onthe counterpart faces at the orifices of the cavities in the blow molds.

Because the blowing and calibration mandrels are short-circuited to oneanother by a hydraulic fluid operated in the spring range, a gentleheight adjustment and in particular a damped delivery of the blowing andcalibration mandrels to the associated blow molds are assured. Thehydraulic short circuit causes a pressure compensation by way of thenumber of blowing and calibration mandrels, which is expressed in thefact that some of the blowing and calibration mandrels are adjusted inone axial direction, while the others are adjusted for compensatorypurposes in the opposite direction.

The blowing and calibration mandrels are advantageously held by clampingin their floating outset position on the beamlike upper machine part.The mount is embodied releasably. A decisive factor for the pressurecompensation over the entire number of blowing and calibration mandrelsis that each blowing and calibration mandrel is held with the sameclamping force. The clamping force is advantageously selected such thatthe blowing and calibration mandrels are secured against unintendedfalling out of their clamping mounts, while their axial heightadjustability is impaired only insignificantly. It is especiallyadvantageous if the clamping force is selected as precisely great enoughthat a correct self-adjustment of the axial height of the blowing andcalibration mandrels once effected is maintained counter to therestoring force of the hydraulic fluid. The clamping force is defined bythe tightening moment of the mounts for the blowing and calibrationmandrels in the beamlike upper machine part, which can be adjusted quitesimply by the operators and maintenance staff, for instance by using asuitable torque wrench. The effective value of the clamping force thendepends on the structural design of the mounting device.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described below in terms of an exemplaryembodiment shown in the drawings. In partly schematic views not toscale, the drawings show:

FIG. 1, a portion of an exemplary apparatus of the invention, with anarrangement of three blowing and calibration mandrels, in their outsetposition;

FIG. 2, the blowing and calibration mandrels of FIG. 1 onceself-adjustment has occurred according to an exemplary embodiment;

FIG. 3, an exemplary upper machine part with an arrangement of twoblowing and calibration mandrels, for the sake of illustrating theirfloating mounting; and

FIG. 4, an exemplary cross section through a blowing and calibrationmandrel taken along the line IV—IV in FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An exemplary apparatus, embodied according to the invention, forproducing hollow bodies, in particular bottles and similar containersprovided with an evacuation opening, of thermoplastic is identified inits entirety in FIG. 1 by reference numeral 1. In particular, thisapparatus is a so-called automatic blow molder, in which the desiredhollow body is produced from a preform by inflation in a mold. Theapparatus 1 includes a lower machine part 2 and a upper machine part 7.The lower machine part 2 is embodied in table-like form and is equippedwith a number of blow molds, which in FIG. 1 are identified by referencenumerals 3 a, 3 b and 3 c. The blow molds 3 a, 3 b and 3 c each encloseone cavity 4, which defines the later form of the hollow body to beproduced. The cavities 4 open out to the top of the table-like lowermachine part 2, where they have orifices 5 oriented toward the uppermachine part 7.

A plurality of blowing and calibration mandrels 8 a, 8 b, 8 c aremounted side by side on the upper machine part 7, which can be embodiedin beamlike form. The number of blowing and calibration mandrels 8 a, 8b, 8 c can correspond to the number of blow molds 3 a, 3 b, 3 c in thelower machine part 2. Each blowing and calibration mandrel is assignedprecisely one blow mold in the embodiment shown. The upper machine part7 is equipped with feeding devices, not identified by reference numeral,with the aid of which the blowing and calibration mandrels 8 a, 8 b, 8 ccan be axially fed jointly toward the blow molds 3 a, 3 b, 3 c in such away that they dip with their calibration regions into the orifices 5 inthe blow molds 3 a, 3 b, 3 c. The feeding motion continues until anencompassing annular shoulder 9 disposed on the blowing and calibrationmandrels 8 a, 8 b, 8 c presses with a predeterminable force against acounterpart face 6 that is provided on each of the blow molds 3 a, 3 b,3 c and that extends around the periphery of the orifice 5 of the cavity4. In this way, material of a preform, and placed in the cavity 4, suchas an inflated single- or multi-layer tube, that protrudes past the blowmolds 3 a, 3 b, 3 c can be pinched off.

The annular shoulders 9 in the exemplary embodiment shown are providedon cutting rings 10 a, 10 b, 10 c, which are mounted interchangeably onthe blowing and calibration mandrels 8 a, 8 b, 8 c.

The cutting rings 10 a, 10 b, 10 c can have different heights r, s, t,which are dictated for instance by production tolerances or result fromdifferent wear. The different heights r, s, t of the cutting rings 10 a,10 b, 10 c are shown somewhat exaggerated in FIG. 1, in order toillustrate the resulting effect clearly. When the annular shoulder 9 ofthe blowing and calibration mandrel 8 a is already pressed against thecounterpart face 6 of the associated blow mold 3 a, the annularshoulders 9 of the other two blowing and calibration mandrels 8 b, 8 care still at the spacing a and b, respectively, from the counterpartfaces 6 of the associated blow molds 3 b, 3 c, because of the lesserheights s, t of the cutting rings 10 b, 10 c. In the apparatuses of theprior art, the height of the blowing and calibration mandrels 8 b, 8 ctherefore had to be changed in an inconvenient adjusting process, inorder to compensate for different heights r, s, t of the cutting rings10 a, 10 b, 10 c and to assure secure pinching off of protrudingmaterial at all the blow molds 3 a, 3 b, 3 c. In this respect it can betaken into account that automatic blow molders can have up to ten oreven more blowing and calibration mandrels with associated blow molds,for the sake of producing hollow bodies on a mass-production basis andeconomically. With the number of blowing and calibration mandrels, theeffort of adjustment naturally also increases. This means downtimes ofthe automatic blow molder that are multiple times longer and also meansan increased risk to operators in the case of adjusting height with themachine running.

In the exemplary apparatus 1 embodied according to the invention, theblowing and calibration mandrels 8 a, 8 b, 8 c each cooperate, on theirrespective end portion supported in the upper machine part 7, withadjusting pistons 12, which are axially displaceable to a limited extentinside bores 13 in the upper machine part 7. The bores 13 communicatewith a conduit 14, which acts as a reservoir for a hydraulic fluid H, byway of which the blowing and calibration mandrels 8 a, 8 b, 8 c areshort-circuited. The hydraulic fluid H is put under pressure in thespring range by the axially adjusted pistons 12.

By the feeding of the blowing and calibration mandrels 8 a, 8 b, 8 cagainst the blow molds 3 a, 3 b, 3 c, the shoulders 9 are supposed to bepressed against the counterpart faces 6. As soon as the shoulder 9 ofthe first blowing and calibration mandrel 8 a is pressed with a certainforce against the counterpart face 6 of the associated blow mold 3 a,the blowing and calibration mandrel 8 a is displaced axially, and theadjusting piston 12 migrates upward. The axial displacement is effectedcounter to the resistance of the hydraulic fluid. The pressuretransmitted to the hydraulic fluid H is distributed, because of theshort circuit, to the adjusting pistons 12 of the other blowing andcalibration mandrels 8 b, 8 c, and as a result these blowing andcalibration mandrels are axially displaced more or less far compared totheir outset position.

FIG. 2 shows the position of the blowing and calibration mandrels 8 a, 8b, 8 c after the self-adjustment. The blowing and calibration mandrel 8a with the cutting ring 10 a having the greatest height r has beenshifted to the rear, into the upper machine part 7. By the pressureexerted on the hydraulic fluid H, the blowing and calibration mandrel 8c with the cutting ring 10 c having the least height t has in turn beenpushed outward in the opposite direction, toward the associated blowmolding mechanism 3 c. The middle blowing and calibration mandrel 8 bhas essentially remained in the same axial position and, with thelocation of its annular shoulder 9, it dictates the set-point locationof the other annular shoulders. The axial height adjustability of theblowing and calibration mandrels 8 a, 8 b, 8 c compared to their outsetposition amounts for instance to about 4 mm (e.g., ±10 percent or moreor less). In a variant of the invention, the axial adjustment range canbe selected as about 2.5 mm. It is understood that even greater heightadjustment ranges can be provided. The hydraulic fluid H has a certainelastic compressibility, which upon initiation of force via the pistons12 brings about a certain damping.

FIG. 3 shows a portion of the upper machine part 7 with two of theblowing and calibration mandrels 8 a, 8 b, preferably disposed inseries, on a larger scale. Identical components have the same referencenumerals as in FIGS. 1 and 2. The blowing and calibration mandrel 8 a onthe left is shown taken apart, to clearly illustrate the structure ofits floating mounting. On the blowing and calibration mandrel 8 b on theright, the elements of its mount are shown in the assembled state. Inthe exemplary embodiment shown, the blowing and calibration mandrels 8a, 8 b are secured to the beamlike upper machine part 7 by a clampingmount such that they float with limited axial displaceability. Theclamping mount comprises a retaining nut 16, which is provided with amale thread and can be screwed into a threaded bore 15 in the uppermachine part 7. The retaining nut 16 cooperates via a conical face 20with a radially compressible clamping element 17. The clamping element17 is preferably a slit cone of an elastic, wear-resistant material, forinstance an industrial plastic. The cone is equipped with a counterpartface 21. The retaining nut 16 and the clamping element 17 are keptprestressed by a cup spring 19, which is braced on one end in thethreaded bore 15 and on the other on an underlay shim 18 placed betweenthe cup spring 19 and the clamping element 17.

The retaining nut 16 is screwed with a predetermined tightening momentinto the threaded bore 15. A torque wrench is used for the purpose, forinstance. The clamping force transmitted to the blowing and calibrationmandrels 8 a, 8 b depends on the force boost by the conical faces 20, 21and the dimensions of the clamping element 17. The effective clampingforce also depends on the coefficients of friction of the cooperatingfaces of the blowing and calibration mandrels 8 a, 8 b and clampingelements 17. In each case, the clamping force should be at least greatenough that the blowing and calibration mandrels 8 a, 8 b do not fallout of their mounts on the upper machine part 7 but instead continue tobe held in floating fashion. Advantageously, the clamping force isprecisely great enough that the automatic axial adjustment of theblowing and calibration mandrels 8 a, 8 b is not significantly hinderedby the hydraulic forces that occur upon feeding toward the lower machinepart. On the other hand, the clamping force suffices to prevent theblowing and calibration mandrels 8 a, 8 b from shifting unintentionallybecause of their weight and the dynamic forces involved in the movementprocesses. The tightening moment for the retaining nut 16 is dependentdirectly on the cone angle selected. As a result, a frictional forcethat is greater than the forces of inertia and that nevertheless stillallows displacement of the blowing and calibration mandrels 8 a, 8 b bythe reaction force in the pinching process is the goal. In a variant ofthe invention, the tightening moment is selected for instance as about20 Nm to about 40 Nm, and preferably about 25 Nm to 35 Nm, andespecially preferably about 31 Nm.

The calibration region at the front of the blowing and calibrationmandrels 8 a, 8 b, in the exemplary embodiment shown, is embodied ineach case by a calibration sleeve 11 mounted interchangeably, forinstance being screwed in. As a result, this sleeve can easily be takenout as needed and replaced. The cutting rings 10 are alsointerchangeably mounted and are braced on a free front end of theblowing and calibration mandrel 8 a, 8 b and on a shoulder on thecircumference of the calibration sleeve 11.

Because of the floating mounting of the blowing and calibration mandrels8 a, 8 b, the possibility also exists as needed of mounting calibrationsleeves 11 with an other than circular cross section, for instanceelliptical calibration sleeves, and orienting them quite simply with thecavities in the blow molds, so that in particular the axes of theblowing and calibration mandrels 8 a, 8 b match the axes of the necks ofthe cavities. To that end, positioning means are provided, which enablea controlled rotation of the blowing and calibration mandrels abouttheir longitudinal axis. The positioning means include an adjusting pin23 in the upper machine part 7, which cooperates with circumferentialknurling or external teeth 22 on the blowing and calibration mandrels 8a, as shown in suggested fashion in FIG. 4. The circumferential knurlingor teeth 22 can have either a uniform or a nonuniform pitch, so that theblowing and calibration mandrels 8 a can be adjusted in rotated fashionin predetermined and even relatively large increments. The adjusting pin23 serves to fix the oriented blowing and calibration mandrel 8 a in theposition set.

It will be appreciated by those skilled in the art that the presentinvention can be embodied in other specific forms without departing fromthe spirit or essential characteristics thereof. The presently disclosedembodiments are therefore considered in all respects to be illustrativeand not restricted. The scope of the invention is indicated by theappended claims rather than the foregoing description and all changesthat come within the meaning and range and equivalence thereof areintended to be embraced therein.

1. An apparatus for producing a hollow body, of thermoplastic, comprising: a lower machine part that has at least two blow molds each provided with a cavity, and beamlike upper machine part, disposed above the lower machine part, on which upper part a number of blowing and calibration mandrels corresponding to the number of blow molds is disposed, each being associated with one blow mold and being jointly feedable toward the blow molds axially and being movable with their calibration region into an orifice of the cavities until an annular shoulder of the blowing and calibration mandrels comes into contact with a counterpart face of the blow molds, the blowing and calibration mandrels being retained in the upper machine part axially freely movably within predeterminable limits, and upon feeding of the blowing and calibration mandrels toward the blow molds, the blowing and calibration mandrels being automatically adjustable in height axially relative to an outset position, counter to resistance of a coupling medium.
 2. The apparatus of claim 1, wherein the blowing and calibration mandrels are coupled hydraulically to one another.
 3. The apparatus of claim 2, wherein the blowing and calibration mandrels cooperate with adjusting pistons, which are limitedly axially displaceable in the upper machine part inside bores and are short-circuited to one another by a hydraulic fluid, which forms the coupling medium, disposed inside a reservoir that communicates with the bores.
 4. The apparatus of claim 3, wherein an axial height adjustability of the blowing and calibration mandrels relative to the outset position amounts to about ±4 mm.
 5. The apparatus of claim 4, wherein the blowing and calibration mandrels are retained by a clamping force of a clamping mount in the beamlike upper machine part and are releasably fixed.
 6. The apparatus of claim 1, wherein an axial height adjustability of the blowing and calibration mandrels relative to the outset position amounts to about ±4 mm.
 7. The apparatus of claim 1, wherein the blowing and calibration mandrels are retained by a clamping force of a clamping mount in the beamlike upper machine part and are releasably fixed.
 8. The apparatus of claim 7, wherein the blowing and calibration mandrels are fixed in their mounts essentially with the clamping force.
 9. The apparatus of claim 8, wherein the clamping mount for the blowing and calibration mandrels includes a retaining nut, which can be screwed into a threaded bore on the upper machine part and which has a male thread, which cooperates via a conical face with a radially compressible clamping element formed as a slit cone of an elastic and wear-resistant material with preferably an industrial plastic, that is provided with a conical counterpart face.
 10. The apparatus of claim 9, wherein the clamping mount includes a prestressing element, which is preferably formed by a cup spring which, upon assembly, is braced on one end in the threaded bore and on the other, with the interposition of an underlay shim, on the clamping element.
 11. The apparatus of claim 1, wherein the blowing and calibration mandrels are retained rotatably about their longitudinal axis in the upper machine part.
 12. The apparatus of claim 11, wherein for rotating each blowing and calibration mandrel about its longitudinal axis, positioning means are provided, which include circumferential knurling or teeth on the blowing and calibration mandrels and an adjusting pin on the upper machine part that is actuatable from outside.
 13. The apparatus of claim 1, wherein the shoulder on each blowing and calibration mandrel is provided on an interchangeably mounted cutting ring.
 14. The apparatus of claim 1, wherein each calibrating portion of the blowing and calibration mandrels is formed by an interchangeable calibration sleeve.
 15. The apparatus of claim 1, wherein the hollow body is a container provided with an evacuation opening.
 16. The apparatus of claim 1, wherein an axial height adjustability of the blowing and calibration mandrels relative to the outset position amounts to about ±2.5 mm.
 17. A method for producing hollow bodies in a hollow body blowing process, comprising: placing preforms extruded in a single layer or multiple layers of a thermoplastic in blow molds; simultaneously inflating by means of a blowing and calibration mandrel assigned to each blow mold, the preforms by overpressure cavities enclosed by the blow molds; calibrating evacuation openings of the hollow bodies; pinching off parts protruding past the evacuation necks during a pinch-off operation, wherein the blowing and calibration mandrels, during the pinching-off operation, in which an annular shoulder on each blowing and calibration mandrel is pressed against a counterpart face on the associated blow mold, are automatically adjusted axially in height relative to an outset position, within predeterminable limits, counter to a restoring force of a coupling medium; hardening the hollow bodies by cooling.
 18. The method of claim 17, comprising: effecting an axial height adjustment of the blowing and calibration mandrels such that the pressure exerted by each annular shoulder on the associated counterpart face is of equal magnitude.
 19. The method of claim 17 comprising: operating a hydraulic fluid operated in the spring range by which the blowing and calibration mandrels are short-circuited to one another, for use as the coupling medium.
 20. The method of claim 17, comprising: retaining the blowing and calibration mandrels are retained by clamping in a mount of a beamlike upper machine part of an automatic blow molder, each blowing and calibration mandrel being held with the same clamping force.
 21. The method of claim 20, the clamping force such that the blowing and calibration mandrels are secured against displacement from their weight and dynamic forces in movement processes, adjustments being in response to hydraulic forces. 